null in JavaScript

C# String.IsNullOrEmpty Javascript equivalent

https://stackoverflow.com/questions/5746947/c-sharp-string-isnullorempty-javascript-equivalent

if(!theString) {
 alert("the string is null or empty");
}

 

扩展

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/null

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typeof null          // "object" (not "null" for legacy reasons) typeof undefined     // "undefined" null === undefined   // false null  == undefined   // true null === null        // true null == null         // true !null                // true isNaN(1 + null)      // false isNaN(1 + undefined) // true

 

作者:Chuck Lu    GitHub